MastemaIf you are looking for an electronic system, I recommend Obsidian or the similar, but free Logseq. As you tag entries it builds a node graph of how your thoughts are connected, which my ADHD really enjoys adding to.
Obsidian is also free if you can manage syncing on your own.
Yes but Logseq is free as in speech as well as free as in beer. Nothing wrong with Obsidian, but if you care about FOSS Logseq is fantastic.